The present invention relates to a fluorescent conversion filter that converts light, emitted by a light-emitting device, in near ultraviolet to visible region light to light in different visible region. The invention also relates to an organic light-emitting device equipped with a fluorescent conversion filter. The fluorescent conversion filter and the organic light-emitting device are applicable to both consumer and industry display apparatuses such as a self-emitting multicolored or full colored-display, a display panel, and a backlight.
Increasing demand for flat panel displays to replace conventional cathode ray tube (CRT) displays, has promoted active development and practical application of various display devices. An electroluminescent device (hereinafter referred to as light-emitting device) is one of the devices created to meet the demand. The light-emitting device has received attention as an all solid state self light-emitting device. The light-emitting device exhibits high resolution and high visibility not readily attained by other display devices.
In a known method for multi-colored or full-colored displays, such as a flat panels, organic light-emitting elements corresponding to the three primary colors of red, blue and green are separately arranged in a matrix form and each of them is caused to emit light. This method is disclosed by Japanese Unexamined Patent Application Publication Nos. S57-157487, S58-147989 and H3-214593. However, the color display using an organic light-emitting device requires precise matrix arrangement of three kinds of light-emitting material for red, blue and green. The technology for this arrangement is difficult and costly to manufacture. Additionally, the chromaticity gradually deviates because the lifetime of the three light-emitting materials differs each other.
In another known method for color display, white light emitted from a backlight is passed through filters and three primary colors are obtained. This method is disclosed by Japanese Unexamined Patent Application Publication Nos. H1-315988, H2-273496 and H3-194895. However, to attain red, green and blue light of high brightness a white-light-emitting device requires high brightness. A white-light emitting device exhibiting both a long life and high brightness has not been obtained yet.
In another known method for color display, fluorescent elements separately arranged in a plane, absorb light from a light-emitting body and each of the fluorescent elements emits multi-colored fluorescent light. This method is disclosed by Japanese Unexamined Patent Application Publication No. H3-152897. This method uses a light-emitting body and fluorescent elements to create multi-colored fluorescent light. This method applied to CRT and plasma display.
In recent years, a color conversion method has been developed in which fluorescent material is used as a filter. The fluorescent material absorbs light from an organic light-emitting element and emits fluorescent light in a visible light region. This method is disclosed by Japanese Unexamined Patent Application Publication Nos. H3-152897 and H5-258860. In this method, the color of the light emitted from the organic light-emitting element is not limited to white light. This method allows use of a brighter organic light-emitting element as a light source. In an example of the color conversion method using an organic light-emitting element emitting blue light, wave length conversion is performed from blue light to green light or to red light. This example is disclosed by Japanese Unexamined Patent Application Publication Nos. H3-152897, H8-286033 and H9-208944.
Organic fluorescent dyes such as rhodamine dye, pyridine dye, oxadine dye and coumarin dye are used for the fluorescent material described above. This use is disclosed by Japanese Unexamined Patent Application Publication Nos. H8-78158, H8-222369, H8-279394, H8-286033, H9-106888, H9-208944, H9-245511, H9-330793 and H10-12379.
Where low energy rays, such as radiation in a near ultraviolet to visible light region, from an organic light-emitting element are used, a full-colored self-emitting display device could be constructed by precisely patterning a fluorescent conversion filter containing such organic fluorescent dye.
There are two methods, among the known methods, for patterning a fluorescent conversion filter. In the first method, similar to the case of inorganic fluorescent material, an organic fluorescent dye is dispersed in a liquid photoresist that is a photo-reactive polymer. The resulting material is then laminated by spin-coating, followed by patterning by means of photolithography. This method is disclosed by Japanese Unexamined Patent Application Publication Nos. H5-198921 and H5-258860.
In the second method, organic fluorescent dye or organic fluorescent pigment is dispersed in a basic binder. The resulting article is then etched by acidic aqueous solution. This method is disclosed by Japanese Unexamined Patent Application Publication No. H9-208944.
The first above-described method of patterning, by means of photolithography, raises a problem where organic fluorescent dye is dispersed in a liquid photoresist. Since the liquid photoresist contains a photopolymerizaion agent, an agent for thermosetting (or polymerization initiator), and a reactive multifunctional monomer or oligomer, decomposition and quenching of the organic dye often occur. Decomposition and quenching of the organic dye can occur due to radicals originated from the photopolymerization initiator or due to propagation radicals of the reactive multifunctional monomer.
The second above-described method of patterning, by means of an acidic aqueous solution, raises a problem when photoresist is coated on the fluorescent conversion filter comprised of a basic binder and later followed by patterning. Since manufacturing a filter requires many steps cost and time are increased. Additionally, as a further disadvantage, this method creates a narrowing of the pattern, caused by side etching.
It is an object of the invention to provide a fluorescent conversion filter that facilitates controlling the radicals originated from the photopolymerization initiator and the propagation radicals of reactive multifunctional monomer in the photolithography process. This will suppress decomposition and quenching of the fluorescent dye.
It is another object of the invention to provide an organic light-emitting device having such a fluorescent conversion filter.
An organic light-emitting device may be equipped with a fluorescent conversion filter which suppresses decomposition and quenching of fluorescent dyes or pigments. The fluorescent conversion filter is formed by coating with a coating material, followed by patterning by photolithography. The coating material consists of a mixture of organic fluorescent dye or pigment that absorbs light in the ultraviolet to visible light region. The coating also includes a photo-setting or photo-and-thermo-setting resin containing a photopolymerizaion initiator of a hydrogen abstraction type having a benzophenone skeleton within the molecule. As a result, an organic light-emitting device is produced by combining the a fluorescent conversion filter with an organic light-emitting element.
According to an embodiment of the invention, there is provided a fluorescent conversion filter comprising: an organic fluorescent dye or an organic fluorescent pigment that absorbs light in a near ultraviolet to visible light region emitted from a light-emitting element, the organic fluorescent dye or pigment emitting different visible light, a matrix resin bearing the organic fluorescent dye or pigment, the resin matrix being a photo-setting resin or a photo-and-thermo-setting resin containing a photopolymerization initiator, the photopolymerization initiator of a hydrogen abstract type, the photopolymerization initiatory having a benzophenone skeleton represented by the following general formula (I) or (II): 
Wherein each of R1 through R10, independently represents a hydrogen atom, a carboxyl group, a hydroxyl group, a nitro group, a halogen atom, an alkyl group of 1 to 6 carbon atoms, an alkoxyl group of 1 to 6 carbon atoms, an aralkyl group of 7 to 18 carbon atoms, an optionally substituted aryl group of 6 to 18 carbon atoms, an optionally substituted aromatic heterocyclic group, an optionally substituted cyclohexyl group, an optionally substituted aryloxyl group, or an optionally substituted pyridyl group. 
Wherein each of R11 through R20, independently represents a hydrogen atom, a carboxyl group, a hydroxyl group, a nitro group, a halogen atom, an alkyl group of 1 to 6 carbon atoms, an alkoxyl group of 1 to 6 carbon atoms, an aralkyl group of 7 to 18 carbon atoms, an optionally substituted aryl group of 6 to 18 carbon atoms, an optionally substituted aromatic heterocyclic group, an optionally substituted cyclohexyl group, an optionally substituted aryloxyl group, or an optionally substituted pyridyl group.
According to another embodiment of the invention there is provided an organic light-emitting device comprising: a fluorescent conversion filter and an organic light emitting element, the organic light emitting element containing an anode patterned on an insulative inorganic oxide film in the fluorescent conversion filter in a set of stripes, the anode composed of electrodes in a pattern, a cathode formed on an electron injection layer, the cathode composed of metal electrodes patterned on the electron injection layer in a set of stripes, the anode stripes disposed orthogonal to the cathode stripes, a hole injection layer covering the anode, a hole transport layer formed on the hole injection layer, an organic light emitting layer formed on the hole transport layer; and an electron injection layer formed on the organic light emitting layer.
The following describes how the fluorescent conversion filter of the invention works. Hardening reaction or polymerization of the photo-setting resin includes radical reaction and ionic reaction. Where the polymerization proceeds by radical reaction, a photopolymerization initiator is necessary, while a photo-sensitizer is sometimes added. There are three types of photopolymerization initiators:
(1) a photo-cleavage type, where a bond is cleaved by a photon to generate two radicals,
(2) a hydrogen abstraction type, where a hydrogen atom is abstracted from a molecule to convert the molecule to a radical, and
(3) an electron transfer type, where an electron(s) transfers between molecules to generate a radical ion.
Experiments determined that, in the action of the radicals to the organic fluorescent dyes, the photo-cleavage type radicals (1) and the electron transfer type radicals (3) interact with an excited dye and are very likely to quench fluorescence in the excited dye. The hydrogen abstraction type initiator (2) rarely affects the excited dye and is not likely to quench fluorescence in the dye.
The present invention has been accomplished based on the finding, and uses the photo-setting resin containing a photopolymerization initiator of a hydrogen abstraction type, having a benzophenone skeleton represented by the general formula (I) or (II) (shown above), as a matrix resin bearing the organic fluorescent dyes or pigments. The use of such photo-setting resin suppresses decomposition and quenching of the fluorescent dye in the photolithography process, to facilitate providing a fluorescent conversion filter with high precision and high conversion efficiency.
The present invention provides a fluorescent conversion filter which absorbs light in a near ultraviolet to visible light region from a light-emitting element and converts the light to a different visible light, for example, red light, with high efficiency. In addition, the fluorescent conversion filter of the invention allows highly precise patterning easily with low cost. An organic light-emitting device equipped with such a fluorescent conversion filter is applicable to commercial-oriented and industry-used display apparatuses, such as a self-lightening multicolored or full-colored display, a display panel, and a backlight. Moreover, a full-colored display device with organic light-emitting elements capable of low voltage driving can be manufactured by equipping such elements with the fluorescent conversion filter of the invention.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.